Temperature dependences for air-broadened Lorentz half-width and pressure shift coefficients in the 30013←00001 and 30012←00001 bands of C[O.sub.2] near 1600 nm

In this study, 39 high-resolution spectra of pure and air-broadened C[O.sub.2] recorded at temperatures between 215 and 294 K were analyzed using a multispectrum nonlinear least-squares technique to determine temperature dependences of air-broadened Lorentz half-width and air-induced pressure shift coefficients for over 100 individual [sup.12]C[sup.16][O.sub.2] transitions in the 30012←00001 (at 6348 [cm.sup.-1]) and 30013←00001 (at 6228 [cm.sup.-1]) bands. Data were recorded with two different Fourier transform spectrometers (Kitt Peak FTS at the National Solar Observatory in Arizona and the Bomem FTS at NRC, Ottawa), with absorption path lengths ranging between 25 and 121 m. The sample pressures varied between 11 torr (pure C[O.sub.2]) and 924 torr (C[O.sub.2]-air) with volume mixing ratios of C[O.sub.2] in air between ~1.5% and 11% (1 torr = 133.322 4 Pa). To minimize systematic errors and increase the accuracy of the retrieved parameters, a constrained multispectrum nonlinear least-squares fitting technique was used to include theoretical quantum mechanical expressions for the rovibrational energies and intensity parameters rather than retrieving the individual positions and intensities line by line. The results suggest no detectable vibrational dependence for the temperature dependences for the air-broadened Lorentz half-width coefficients and the air-induced pressure shift coefficients. The half-width coefficients and temperature dependence exponents were modeled using semiclassical calculations based upon the Robert-Bonamy formalism. A good agreement is seen between the measurements and theoretical calculations. Beyond |m| = 26, a simple scaling factor (0.96) has been applied to the calculated half-width coefficients to match the experimental measurements. PACS Nos: 32.70.Jz, 33.70.Jg, 33.20.Ea Trente-neuf spectres de C[O.sub.2] elargis par l'air ont ete enregistres a haute resolution et entre 215 et 294 K. Leur analyse par une technique de moindres carres multi-spectres non-lineaires a permis de determiner la dependance en temperature des coefficients d'elargissement Lorentzien et des coefficients de deplacement induits par l'air pour plus de 100 transitions individuelles de [sup.12]C[sup.16][O.sub.2] dans les bandes 30012←00001 (a 6348 [cm.sup.-1]) et 30013←00001 (a 6228 [cm.sup.-1]). Les spectres ont ete enregistres avec deux spectrometres a transformee de Fourier differents (le FTS du National Solar Observatory a Kitt Peak en Arizona, et le FTS Bomem du CNRC a Ottawa) et avec des chemins d'absorption variant de 25 a 121 m. La pression des echantillons s'etendait de 11 torr (C[O.sub.2] pur) a 924 torr (C[O.sub.2]-air) avec des rapports de melange compris entre ~1.5% et 11% (1 torr = 133,3224 Pa). Pour diminuer les erreurs systematiques et accroitre la precision des parametres determines, une technique de moindres carres multi-spectres, incluant une contrainte basee sur l'expression quantique de la dependance rovibrationelle des energies et intensites des raies, a ete utilisee plutot que des determinations individuelles raie par raie. Les resultats suggerent l'absence de dependance vibrationnelle pour la dependance en temperature des coefficients d'elargissement et de deplacement induits par l'air. Les coefficients d'elargissement et de dependance en temperature ont ete modelises par une methode semi-classique basee sur le formalisme de Robert-Bonamy. Un bon accord a ete trouve entre les resultats mesures et calcules. Pour |m| en dessus de 26, un simple facteur d'echelle (0,96) a ete utilise pour que le calcul des coefficients d'elargissement corresponde aux observations. [Traduit par la Redaction]
1. Introduction The Earth's atmosphere bears the fingerprint of human influences. Our knowledge and understanding of spatial and temporal patterns in the Earth's carbon cycle, and ultimately of global warming [...]